Dynamic Insights

Optical slow-motion recordings provide insights into dynamic processes. But they show only processes that are actually visible; what happens inside objects during such processes remains unclear. This is where high-speed X-ray detectors come into play. The Fraunhofer Development Center for X-ray Technology EZRT is opening up completely new possibilities for analyzing dynamic processes by means of a synchronous and same-perspective combination of optical high-speed imaging and X-ray imaging.

 

With a loud bang, a car hits a bollard wrapped in bright warning colors. The plastic of the bumper splinters and the car body deforms, almost elegantly wrapping itself around the obstacle. In behaving as they did, the materials responded precisely as the vehicle designers intended. A meticulously prepared crash test like this is designed to demonstrate the correct engineering and safety of the vehicle – a way to show that all the previous calculations and simulations were on the mark.

To this end, the deformation of the vehicle is recorded exactly as it happened using high-speed optical cameras. Examining one image at a time, the experts can piece together how the test matches up with the calculations. Their aim is to make sure that the material on the outside of the vehicle deforms precisely as planned in order to provide maximum protection for hypothetical occupants.

But what, exactly, happens inside the vehicle at the moment of impact? How do the load-bearing structures change? Are the forces transmitted and distributed to the various components as intended? Engineers are desperate to get the answers to such questions. In collaboration with researchers from the Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut, EMI, the Fraunhofer-internal research project MAVO fastXcrash aims to develop basic principles that will provide answers to questions like these.

XEye: A look inside at over 1000 frames per second

A key component is the X-ray detector, which, in conjunction with the X-ray source, is responsible for the quality of the X-ray images produced. Researchers at the Fraunhofer Development Center for X-ray Technology EZRT have developed a technology that, depending on the energy of the X-ray source, can be used to produce high-speed X-ray images of almost any size. And it can do this at high resolution, at up to 6000 frames per second and with pixel sizes starting at 200 μm. If such high speeds are not required, more detailed images can also be provided starting at a pixel size of 45 μm. The key is the patented XEye technology developed at the Fraunhofer EZRT, which enables X-ray detectors with, for example, an active area of

1.2 m × 0.8 m and a pixel size of 400 μm. The sensitivity of these detectors has been increased to such an extent that even with standard industrial X-ray sources at 1000 frames per second, the image quality they achieve is sufficient to analyze internal processes, depending on the object to be X-rayed. Previously, modeling clay was laboriously added as an indicator to analyze the extent to which a component deforms or moves; now, a digital high speed recording tracks the process more quickly, reliably and in greater detail.

By additionally using the VEye detector in front of the X-ray tube, high-speed optical images can be created from the perspective of the XEye X-ray detector. This enhances understanding of the internal structures.

 

 

“The findings are promising and provide valuable insights – especially for the advanced development of new products.”

Dr. Norman Uhlmann, division director of Fraunhofer EZRT

 

Added value for product development

One of the first practical applications of this technology came in collaboration with the Fürth-based sporting goods manufacturer UVEX Sports. In crash tests with an artificial skull, the material of a bicycle helmet had to demonstrate that it behaved as the designers expected to provide the wearer with the best possible protection in an emergency.

Numerous sectors set to benefit

In addition to failure and deformation analyses, the method is also suitable for observing flow or mixing processes. What is the ideal distribution of hot water in an espresso machine’s portafilter to create the best-tasting coffee? To answer questions such as these, the technology can be combined with computed tomography to record a change in volume over a period of time. This method, also known as 4DCT, allows volume changes to be recorded on a second-by-second basis, which makes it possible to visualize the water flow through the ground coffee in 3D. Construction of a 4DCT demonstrator to answer these and other exciting questions is currently underway in the EZRT’s laboratories, and perhaps at some point in the future it will be possible to record a car crash test in 4D as well.

 

X-ray-Movie: Breaking Bottle

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X-ray-Movie: Bicycle Helmet

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How does X-ray technology improve the crema on your espresso?

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